The present invention relates to an ablation catheter for treatment of cardiac arrhythmia, for example atrial fibrillation. More particularly, it relates to an ablation catheter configured to electrically isolate a vessel, such as a pulmonary vein, from a chamber, such as the left atrium with a continuous lesion pattern and a method for forming such a lesion pattern.
The heart includes a number of pathways that are responsible for the propagation of signals necessary to produce continuous, synchronized contractions. Each contraction cycle begins in the right atrium where a sinoatral node initiates an electrical impulse. This impulse then spreads across the right atrium to the left atrium, stimulating the atria to contract. The chain reaction continues from the atria to the ventricles by passing through a pathway known as the atrioventricular (AV) node or junction, which acts as an electrical gateway to the ventricles. The AV junction delivers the signal to the ventricles while also slowing it, so the atria can relax before the ventricles contract.
Disturbances in the heart""s electrical system may lead to various rhythmic problems that can cause the heart to beat irregularly, too fast or too slow. Irregular heart beats, or arrhythmia, are caused by physiological or pathological disturbances in the discharge of electrical impulses from the sinoatrial node, in the transmission of the signal through the heart tissue, or spontaneous, unexpected electrical signals generated within the heart. One type of arrhythmia is tachycardia, which is an abnormal rapidity of heart action. There are several different forms of atrial tachycardia, including atrial fibrillation and atrial flutter. With atrial fibrillation, instead of a single beat, numerous electrical impulses are generated by depolarizing tissue at one or more locations in the atria (or possibly other locations). These unexpected electrical impulses produce irregular, often rapid heartbeats in the atrial muscles and ventricles. Patients experiencing atrial fibrillation may suffer from fatigue, activity intolerance, dizziness and even strokes.
The precise cause of atrial fibrillation, and in particular the depolarizing tissue causing xe2x80x9cextraxe2x80x9d electrical signals, is currently unknown. As to the location of the depolarizing tissue, it is generally agreed that the undesired electrical impulses often originate in the left atrial region of the heart. Recent studies have expanded upon this general understanding, suggesting that nearly 90% of these xe2x80x9cfocal triggersxe2x80x9d or electrical impulses are generated in one (or more) of the four pulmonary veins (PV) extending from the left atrium. In this regard, as the heart develops from an embryotic stage, left atrium tissue may grow or extend a short distance into one or more of the PVs. It has been postulated that this tissue may spontaneously depolarize, resulting in an unexpected electrical impulse(s) propagating into the left atrium and along the various electrical pathways of the heart.
A variety of different atrial fibrillation treatment techniques are available, including drugs, surgery, implants, and catheter ablation. While drugs may be the treatment of choice for some patients, drugs typically only mask the symptoms and do not cure the underlying cause. Implantable devices, on the other hand, usually correct an arrhythmia only after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem by ablating the abnormal tissue or accessory pathway responsible for the atrial fibrillation. The catheter-based treatments rely on the application of various destructive energy sources to the target tissue, including direct current electrical energy, radiofrequency electrical energy, laser energy, and the like. The energy source, such as an ablating electrode, is normally disposed along a distal portion of a catheter.
Most ablation catheter techniques employed to treat atrial fibrillation focus upon locating the ablating electrode, or a series of ablating electrodes, along extended target sections of the left atrium wall. Because the atrium wall, and thus the targeted site(s), is relatively tortuous, the resulting catheter design includes multiple curves, bends, extensions, etc. In response to recent studies indicating that the unexpected electrical impulses are generated within a PV, efforts have been made to ablate tissue within the PV itself. Obviously, the prior catheter designs incorporating convoluted, multiple bends are not conducive to placement within a PV. Instead, a conventional xe2x80x9cstraight endedxe2x80x9d ablation catheter has been employed. While this technique of tissue ablation directly within a PV has been performed with relatively high success, other concerns may arise.
More particularly, due to the relatively small thickness of atrial tissue formed within a PV, it is likely that ablation of this tissue may in fact cause the PV to shrink or constrict. Because PV""s have a relatively small diameter, a stenosis may result. Even further, other vital bodily structures are directly adjacent each PV. These structures may be undesirably damaged when ablating within a PV.
In light of the above, an alternative technique has been suggested whereby a continuous ablation lesion pattern is formed in the left atrium wall about the ostium associated with the PV in question. In other words, the PV is electrically isolated from the left atrium by forming an ablation lesion pattern that surrounds the PV ostium. As a result, any undesired electrical impulse generated within the PV could not propagate into the left atrium, thereby eliminating unexpected atria contraction.
Unfortunately, while PV isolation via a continuous ablation lesion pattern about the PV ostium appears highly viable, no acceptable ablation catheter configuration exists. Most atrial fibrillation ablation catheters have linear distal ends, designed for manipulation in a sliding fashion along the atrial wall. That is to say, the distal, electrode-carrying end of the catheter is typically slid along (or parallel to) the atrial wall. With this generally accepted configuration in mind, it may be possible to shape the distal, electrode-carrying end into a small ring sized in accordance with the PV ostium. For example, U.S. Pat. No. 5,617,854 discloses one such possibility. More particularly, the described ablation catheter includes a substantially ring-shaped portion sized to contact the ostium of the coronary sinus. Pursuant to conventional designs, the ring extends linearly from the catheter body. In theory, the ring-shaped portion may be placed about a PV ostium. However, proper positioning would be extremely difficult and time consuming. More particularly, it would be virtually impossible to locate and then align the ring about a PV ostium when sliding the catheter along the atrium wall. The ring must be directed toward the ostium in a radial direction (relative to a central axis of the ostium). Even if the electrophysiologist were able to direct the ring to the ostium, the periodic blood flow through the PV would likely force the ring away from the atrium wall, as the catheter body would not provide any support.
A related concern entails mapping of a PV prior to ablation. In cases of atrial fibrillation, it is necessary to identify the origination point of the undesired electrical impulses prior to ablation. Thus, it must first be determined if the electrical impulse originates within one or more PVs. Once the depolarizing tissue has been identified, necessary ablation steps can be taken. Mapping is normally accomplished by placing one or more mapping electrodes into contact with the tissue in question. In order to map tissue within a PV, therefore, a relatively straight catheter section maintaining two or more mapping electrodes must be extended axially within the PV. Ablation catheters configured to slide along the atrial wall cannot include a separate, distal extension for placement within the PV. Instead, an entirely separate mapping catheter must be provided and then removed for subsequent replacement with the ablation catheter. Obviously, these additional steps greatly increase the overall time required to complete the procedure.
Electrical isolation of a pulmonary vein via an ablation lesion pattern surrounding the pulmonary vein ostium presents a potentially revolutionary technique for treatment of atrial fibrillation. However, the unique anatomical characteristics of a pulmonary vein and left atrium render currently available ablation catheters minimally useful. Therefore, a substantial need exists for an ablation catheter designed for consistent positioning of one or more ablation electrodes about a pulmonary vein ostium, as well as for providing pulmonary vein mapping information.
One aspect of the present invention provides a catheter assembly for treatment of cardiac arrhythmia. The catheter assembly includes a catheter body and at least one electrode. The catheter body includes a proximal portion, an intermediate portion and a distal portion. The intermediate portion extends from the proximal portion and defines a longitudinal axis. The distal portion extends from the intermediate portion and forms a substantially closed loop transverse to the longitudinal axis. The electrode is disposed along the loop. With this configuration, upon activation, the electrode ablates a continuous lesion pattern in a plane substantially perpendicular to the longitudinal axis. When placed about an ostium of a vessel associated with a chamber formed within a patient, the continuous lesion pattern established by the electrode electrically isolates the vessel from the chamber. For example, the catheter assembly may be provided for treatment of atrial fibrillation whereby the lesion pattern in formed to electrically isolate a pulmonary vein (vessel) from the left atrium (chamber). In one preferred embodiment, the catheter assembly further includes a mapping device for mapping tissue within the vessel.
Another aspect of the present invention relates to a catheter assembly for treatment of cardiac arrhythmia. The catheter assembly comprises a catheter body and at least one electrode. The catheter body includes a proximal portion, an intermediate portion and a distal portion. The intermediate portion extends from the proximal portion and defines a longitudinal axis. The distal portion extends from the intermediate portion and forms a substantially closed loop. The loop defines a loop axis substantially parallel to the longitudinal axis. The electrode is disposed along the loop. With this configuration, upon energization, the electrode ablates a continuous lesion pattern in a plane substantially perpendicular to the longitudinal axis. When placed in contact with tissue, the electrode ablates a continuous lesion pattern, isolating tissue within the lesion pattern. For example, the catheter assembly may be provided for treatment of atrial fibrillation whereby the lesion pattern is formed to electrically isolate a pulmonary vein from the left atrium. In one preferred embodiment, the catheter assembly further includes a mapping device extending distal the loop for mapping tissue.
Another aspect of the present invention relates to a method for forming an ablation pattern to electrically isolate a vessel, defining an ostium, from a chamber formed within a patient for treatment of cardiac arrhythmia. The method includes selecting a catheter assembly comprising a catheter body and at least one electrode. The catheter body defines a longitudinal axis and includes a proximal portion and a distal portion. The distal portion forms a substantially closed loop transverse to the longitudinal axis, the loop defining a loop axis substantially parallel to the longitudinal axis. The electrode is disposed along the loop. The distal portion of the catheter body is guided into the chamber and is directed to a position spaced from the vessel ostium, with the loop axis being substantially aligned with a center of the vessel ostium. The distal portion is advanced in a direction parallel with the loop axis such that the loop contacts the chamber wall about the vessel ostium. Finally, the electrode is energized to ablate a continuous lesion pattern about the vessel ostium to electrically isolate the vessel from the chamber. For example, the method may be utilized to electrically isolate a pulmonary vein (vessel) from the left atrium (chamber) by forming a lesion pattern about the pulmonary vein ostium. In one preferred embodiment, the method further includes mapping the vessel with a mapping electrode.
Yet another aspect of the present invention relates to a method of electrically isolating a vessel from a chamber formed within a patient, the vessel defining an ostium in a wall of the chamber, for treatment of cardiac arrhythmia. The method includes ablating a continuous, closed lesion pattern in the chamber wall about the vessel ostium. The lesion pattern electrically isolates the vessel from the chamber. For example, the method may be utilized to electrically isolate a pulmonary vein from the left atrium.